Yes, water can go ‘stale’. No, drinking it (probably) isn’t bad for you

Whether it's that bottle you leave by your bed to wet your whistle in the wee hours or the glass you left half-full on your desk yesterday, you'll know that water that's not poured fresh out of the tap or mineral water bottle can taste a little… musty.

That stale taste can cause our brain to start conjuring images of bacteria and germs so Coach called up Dr Rico Tabor, senior chemistry lecturer at Monash University to find out whether it's cause for concern.

Natural forces at play

If you're used to drinking refrigerated water then you'll notice the flavour change as it warms to room temp.

"You’re much more sensitive to flavours once it’s warmed up," Dr Tabor explains.

"It will also absorb a little bit of carbon dioxide from the air, which decreases the pH a little bit so it makes it a tiny bit more acidic and gives it a slightly different flavour. Think very diluted soda water, which has a slightly different flavour."

With tap water, the taste can also change as the chlorine evaporates.

"The chlorine tends to mask any other flavours present," Dr Tabor says.

"Half an hour is enough for the chlorine to just disappear from the water into the air."

(Forget fancy filters – there's a good tip if you want to de-chlorinate your water!)

As your water warms and the chlorine disappears, you'll get hints of organic molecule flavour that Dr Tabor says come from soil microbe processes.

"Geosmin is the molecule that creates that beautiful smell after it rains," he points out.

"Geosmin exists naturally in tap water in very low concentrations but you can't detect it when it's being masked by chlorine or when it's cold. Once the water warms up and the chlorine disappears, the tap water can taste a bit earthy.

“Those organic problems are really no problem at all – tap water is certainly not bad for you."